Apparatus for regulating tension in sheet material

ABSTRACT

Tension in sheet material leaving a pair of cylinders of a machine, particularly a rotogravure machine, is regulated by varying the speed of one of the cylinders according to the changes in position of a jockey roller tensioning the sheet.

United States Patent [1 1 Corse 1 Sept. 16, 1975 1 1 APPARATUS FOR REGULATING TENSION IN SHEET MATERIAL [75] lnventor: Louis Corse, Orleans, France [73] Assignee: Societe dEtudes de Machines Speciales, France 221 Filed: Jail. 9, 1974 [21] Appl. No.: 431,978

[30] Foreign Application Priority Data Jan. 11, 1973 France 73.00898 [52] US. Cl 226/44; 101/228 [51 Int. Cl B65h 25/04 [58] Field of Search 226/44, 30, 42, 114, 1;

lOl/DIG. 21, 225, 228

[56] References Cited UNITED STATES PATENTS 2,586,286 2/1952 Andreas 226/44 X 3,087,663 5/1963 Anderson 226/44 3,165,056 l/1965 Hcatlcy 226/42 X 3,587,959 6/1971 G1over..... 226/44 X 3,734,368 5/1973 Kudelski 226/44 Primary ExaminerRichard A. Schacher Alturney, Agent, or FirmRobert E. Burns; Emmanuel J. Lobato; Bruce L. Adams 5 7] ABSTRACT Tension in sheet material leaving a pair of cylinders of a machine, particularly a rotogravure machine, is regulated by varying the speed of one of the cylinders according to the changes in position of a jockey roller tensioning the sheet.

1 Claim, 1 Drawing Figure BACKGROUND OF THE INVENTION The present invention relates to rotary printing apparatus having means for regulating the tension of a sheet of material moving between two cylinders of which one is covered with a flexible material such as rubber. The invention can he applied particularly in a rotary press of the photogravure type. A press of this type consists of a succession of printing stations, at each of which there is a pair of cylinders, i.e. an engraved plate or printing cylinder which is driven in rotation and an impression cylinder of flexible material, parallel and tan gential to the first cylinder and generally freely mounted.

The plate cylinder is immersed in a trough of ink while the impression cylinder is pressed against the plate eylinder either manually or by means of pneumatic or hydraulic jacks.

To ensure-even printing in a rotogravure press the sheet of material has to be tensioned between two successive printing stations. To obtain this tension a number of methods may be adapted.

In a first known method, use is made of plate cylin ders of increasing diameter from the first station of apparatus onwards, in such a Way that the rate of delivery likewise increases from one station to the next, thus ensuring the required tension. This system suffers from a major drawback if the sheet of material is non-ductile,

particularly in the case of annealed aluminium, which is not elastic and which retains a permanent elongation, which should not exceed 1/1000. Now in the case of a whole series of rotogravure units, this value may be considerably exceeded.

In another known method the pressure of the impression cylinder is varied, and it presses to a varying extent against the plate cylinder, and according to the force of the pressure and as a result of the deformations undergone by the rubber and the internal tensions in the sheet of material a vermicular sliding action occurs, in such a way that the rate of output decreases in accordance with the increase in pressure.

This method is applied by the aid of means situated between each pair of printing stations, which scans the tension of the sheet and which acts accordingly on the pressure of the impression cylinder of the preceding unit of apparatus. This device suffers from a major disadvantage, i.e. from the fact that it does not enable the pressure to be regulated to establish the pressure value desired in order to obtain satisfactory prints.

The object of the present invention is to eliminate these drawbacks by providing means for the regulation of the tension of a sheet of material moving between two units of apparatus, particularly of a rotary press of the photogravure type, confining this tension to certain levels not causing any elongations beyond a certain permissible limit.

SUMMARY OF THE INVENTION The invention is characterized by the fact that the variation in the tension of the sheet of material, downstream the pair of cylinders, in one sense or in the other in relation to a certain prescribed value. is compensated by effecting a correlative variation in the rotation speed of the said impression cylinder in relation to that of a driven cylinder plate to which it is tangential.

The essential advantage of such a process and of the device for its performance resides in the fact that it requires no recourse to any action on the parameter consisting of the pressure of the impression cylinder against the sheet of material to be printed. This action remains fully under the control of the printer, who may utilize it for any other regulating operation within the printing process.

DESCRIPTION OF DRAWING The drawing shows a schematic diagram of a machine fitted with the device according to the invention.

DESCRIPTION OF PREFERRED EMBODIMENT Referring to the single figure of the drawing, a rotary photogravure press (only the elements of which relevant to the invention are depicted) comprises an upstream printing station including an engraved plate cylinder l which runs in a trough of ink 2. This cylinder I is driven by a motor Ia, and coacts with an impression cylinder 3 having a rubber surface to print in one colour on a sheet of material 4 passing between the two cylinders. The sheet 4 passes from the cylinders l and 3 to a downstream printing station in which is passes between a plate cylinder 6 and an impression cylinder 5, so to be printed with a second colour by ink from a separate trough 2.

To ensure that the sheet passes satisfactorily between the two printing stations, and the printed images register with each other, the sheet is tensioned by means 7 including ajockey roller 7b which engages a loop 4 of sheet between two cylinders 7a and 7('. A weight 8, or alternatively a spring or other means, urges the jockey roller downwards to tension the sheet to a desired degree.

The impression cylinder 3 is positively driven by a control device 10 powered by the driven plate cylinder 1 for example, via suitable transmission systems. Normally, the cylinders l and 3 rotate at identical speeds.

The jockey roller 7b is interconnected by way of a linkage 9 such as a differential or other device consisting of a system of levers 9a on a change speed mechanism 9b interposed in the transmission between the two cylinders.

This speed control device is arranged in such a way that if the tension of the sheet 4 varies in either sense from a preset standard, so that the tensioning device 8 changes in position or shape, in order to balance out the deviation in the tension of the sheet 4, the said device 8 also acts on the speed control device 9!), in order to vary the speed of the impression cylinder 3 slightly with respect to the engraved plate cylinder 1.

This change in the speed of the impression cylinder 3 causes in the sheet 4 compensatory tension variations of the opposite sense to those aforementioned. The sheet tension is thereby automatically restored to normal. For example, if the tension of the sheet 4, between the jockey cylinder 71; and the downstream printing station undergoes a slight increase, the cylinder 7b rises and the tensioning device 8 which likewise rises or increases in length, effects a displacement of the system of levers 9a, acting on the speed change mechanism 9b, in such a way that the speed of the impression cylinder 3 of the upstream printing station is increased slightly in relation to that of the driven cylinder 1. This will result in a reduction in the tension downstream of the cylinders l, 3. In consequence of this action the jockey roller 7b once again drops and moves the tensioning device 8, the levers 9a and the speed variator 9b in the opposite direction. Equilibrium is thus re-established. the tension in the sheet 4 being again restored to the preset standard. The operation obviously takes place in the converse direction. again restoring the equilibrium and the normal tension in the sheet 4. when the tension between the jockey roller 7/; and the downstream printing station decreases. the jockey cylinder 7h falling.

, The sensitivity of this device for adjusting the tension in the sheet 4 is such that a variation in the tension of the latter can never exceed permissible limits, no matter how restricted these may be. It is sufficient to set the tension at the outset to a certain normal initial level for the typeof material of the sheet 4 to be printed, and the device then acts automatically, limiting the tension deviations in the sheet to the permissible limits.

As the device to which the invention relates does not regulate the tension by varying the pressure P of the impression cylinder 3 on the plate cylinder 1, variation in this pressure can be effected by pressure control means P a independent of speed control means gb, 10. Such variation remains totally within the control of the user ofthe machine, who can accordingly regulate the printing conditions in the most satisfactory possible manner.

The device described above can obviously be constructed in accordance with numerous alternative embodiments within the spirit and scope of the invention as regards, for example, the tensioning device 8, the speed control device 9 or the method of controlling the impression cylinder 3 from the plate cylinder 1 or the main shaft of the machine. These differences in construction. however. do not affect the principle of the invention.

i claim:

1. In a printing system: means for imprinting an elongate sheet and for delivering the imprinted. elongate sheet, comprising a rigid engraved plate cylinder having power means for rotating it at a first speed and a flexible impression cylinder having power means for rotating it at a second speed correlated with said first speed, said cylinders having parallel axes; pressure means for pressing one of the cylinders against the sheet and thereby against the other cylinder; means for maintaining a loop in the delivered sheet; jockey roll means biased for engaging the loop to maintain tension therein and to respond to variations in said tension by movements of the jockey roll means to different positions to compensate said variations in tension; and. control means controlled by the jockey roll means for responding to the movements thereof and for thereby controlling one of the power means to vary one of said speeds relative to the other speed so as to compensate said movements of the jockey roll means; 1 thereby enabling regulation of said tension independently of said pressure means. 

1. In a printing system; means for imprinting an elongate sheet and for delivering the imprinted, elongate sheet, comprising a rigid engraved plate cylinder having power means for rotating it at a first speed and a flexible impression cylinder having power means for rotating it at a second speed correlated with said first speed, said cylinders having parallel axes; pressure means for pressing one of the cylinders against the sheet and thereby against the other cylinder; means for maintaining a loop in the delivered sheet; jockey roll means biased for engaging the loop to maintain tension therein and to respond to variations in said tension by movements of the jockey roll means to different positions to compensate said variations in tension; and control means controlled by the jockey roll means for responding to the movements thereof and for thereby controlling one of the power means to vary one of said speeds relative to the other speed so as to compensate said movements of the jockey roll means; thereby enabling regulation of said tension independently of said pressure means. 